A number of disorders are characterized by formation of stenosis, strictures, or aneurysms that prevent normal passage and draining of fluids in body blood vessels and other tubular body structures, such as the esophagus, bile and kidney ducts, urinary tract, gastrointestinal (GI) tract, sinus pathway, and the tracheo-bronchial tree. When a tubular body structure becomes occluded, it is often desirable to dilate the occluded area and facilitate drainage of fluids therethrough. Although surgical methods are available for removing an occlusion or for a complete removal of a narrowed area and restoring normal fluid flow, it involves general anesthesia that may not be suitable for all patients and may also result in formation of secondary strictures from local surgical scars. Some of such secondary strictures may not be amendable to further surgery due to their difficult location or due to the underlying patient condition.
An alternative treatment that avoids many complications of a surgery, involves a two-step procedure in which stricture is first dilated and then a stent is inserted. Typically, stents are longitudinal cylindrical devices formed of biocompatible material, such as metal or plastic. Although conventional stents usually allow a patient to avoid a surgical treatment, they have several limitations. For example, when metal stents are used to treat occlusions in biliary or procreatic ducts, they cannot be removed or replaced. When left in place, they often lead to development of sludge and epithelial proliferation that result in severe stricture and restenosis of the biliary system at the stent site. Accordingly, conventional metal stents are usually used in patients with malignant tumors who are not expected to survive for a prolonged period of time.
The presently available plastic stents for treatment of occlusions in biliary or procreatic ducts also have significant limitations. They are stiff and once inserted percutaneously, the drain usually runs in the intercoastal space and leads to a significant discomfort to the patient. Furthermore, similarly to the metal stents, plastic stents often cause a premature occlusion from sludge and stone formation, which may result in a biliary infection. Although these stents provide significant dilatation of the biliary system, they lead to significant recurrence of the stricture in over 50% of the patients.